1. Field of the Invention
The present invention relates to a multilayer ceramic electronic component and a method for manufacturing the multilayer ceramic electronic component and, in particular, to a multilayer ceramic electronic component in which external electrodes are directly formed on the surface of a laminate by plating and a method for manufacturing the multilayer ceramic electronic component.
2. Description of the Related Art
As illustrated in FIG. 3, a multilayer ceramic electronic component 101, such as a multilayer ceramic capacitor, generally includes a laminate 102, which includes ceramic layers 103 and internal electrodes 104 and 105 alternately disposed between the ceramic layers 103. An end of each of the internal electrodes 104 is exposed at an end surface 106 of the laminate 102. An end of each of the internal electrodes 105 is exposed at an end surface 107. External electrodes are formed on the end surfaces 106 and 107 to electrically connect the corresponding ends of the internal electrodes 104 and 105.
Typically, the external electrodes are formed as follows. First, a metal paste including a metal component and a glass component is applied to the end surfaces 106 and 107 of the laminate 102 and is baked to form paste electrode layers 108 and 109. First plated layers 110 and 111 made primarily of, for example, Ni are then formed on the paste electrode layers 108 and 109. Second plated layers 112 and 113 made primarily of, for example, Sn are then formed on the first plated layers 110 and 111. Thus, the external electrodes have a three-layer structure including the paste electrode layers 108 and 109, the first plated layers 110 and 111, and the second plated layers 112 and 113.
The external electrodes are required to have good solder wettability so that the multilayer ceramic electronic component 101 can be securely soldered to a substrate. The external electrodes are also required to electrically connect the corresponding internal electrodes, which are insulated from each other. The second plated layers 112 and 113 provides good solder wettability to the multilayer ceramic electronic component 101. The paste electrode layers 108 and 109 electrically connect the internal electrodes 104 and 105. The first plated layers 110 and 111 prevent solder leaching.
However, the paste electrode layers 108 and 109 have a relatively large thickness such as several tens to several hundreds of micrometers. Thus, in a multilayer ceramic electronic component 101 having a specified volume, the paste electrode layers 108 and 109 reduce the effective volume for capacitance. In contrast, the first plated layers 110 and 111 and the second plated layers 112 and 113 have a relatively small thickness such as several micrometers. Accordingly, if the external electrodes are formed only of the plated layers, the effective volume for capacitance can be increased.
For example, Japanese Unexamined Patent Application Publication No. 63-169014 discloses a method for depositing an electroconductive metal layer by electroless plating on side surfaces of a laminate at which internal electrodes are exposed so that the exposed internal electrodes are connected to each other.
However, in this method, a plating solution tends to enter the laminate from the side surfaces at which the internal electrodes are exposed. Heat treatment to remove water in the plating solution after plating may cause blisters on the surface of a plated layer, thus impairing the appearance. The plated layer in contact with a side surface at which the internal electrodes are exposed should have a thickness of at least about 5 μm to ensure an electrical connection between the internal electrodes. However, the number of blisters increases significantly with the thickness of the plated layer increases.